Add/Sub

add : Register2 = Register2 + Register1
sub : Register2 = Register2 - Register1

Affected Flags
C	V	N	Z
X	X	X	X

The add and sub instructions are used for addition and substraction.The operation is performed between two registers and the result is put in the last one.

Forms and variants

rx = source register
ry = destination register

Form	Effect
add.b ry,rx	rx <- rx + ry
add.w ry,rx
add.l ry,rx
sub.b ry,rx	rx <- rx - ry
sub.w ry,rx
sub.l ry,rx

Instruction encoding

S = Source register number
D = Destination register number

Instruction	Op Code	Cycles	Encoding
add.b ry,rx	0E	6	00001110 SSSSDDDD
add.w ry,rx	4E	6	01001110 SSSSDDDD
add.l ry,rx	8E	6	01001110 SSSSDDDD
sub.b ry,rx	0F	6	00001111 SSSSDDDD
sub.w ry,rx	4F	6	01001111 SSSSDDDD
sub.l ry,rx	8F	6	10001111 SSSSDDDD

Code Examples

Note: This example is for understanding and can be optimized.

// Example : Simple (naive) Checksum of a c-style text string

; r0 = pointer to string (in)
; r0 = result (out)

checksum: pushregs r1-r2
          movex.b #0,r1
loop:     move.b(r0),r2
          beq out
          inc #1,r0
          add.b  r2,r1
          bra loop
out:      move.b r1,r0
          popregs r1-r2
          rts

Add/Sub

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